Method of determining a target mesa configuration of an electrostatic chuck

ABSTRACT

A method of modifying the heat transfer coefficient profile of an electrostatic chuck by configuring the areal density of a mesa configuration of an insulating layer of the chuck is provided. A method of modifying the capacitance profile of an electrostatic chuck by adjustment or initial fabrication of the height of a mesa configuration of an insulating layer of the chuck is further provided. The heat transfer coefficient at a given site can be measured by use of a heat flux probe, whereas the capacitance at a given site can be measured by use of a capacitance probe. The probes are placed on the insulating surface of the chuck and may include a plurality of mesas in a single measurement. A plurality of measurements made across the chuck provide a heat transfer coefficient profile or a capacitance profile, from which a target mesa areal density and a target mesa height are determined. The target density and height are achieved mechanically; the target density by mechanically adjusting the areal density of existing mesas; and the target height by creating or deepening low areas surrounding planned or existing mesas, respectively. This can be accomplished using any of known techniques for controlled material removal such as laser machining or grit blast machining on an X-Y table.

BACKGROUND

As semiconductor technology progresses, decreasing transistor sizes callfor an ever higher degree of accuracy, repeatability and cleanliness inwafer processes and process equipment. Various types of equipment existfor semiconductor processing, including applications that involve theuse of plasmas, such as plasma etch, plasma-enhanced chemical vapordeposition (PECVD) and resist strip. The types of equipment required forthese processes include components which are disposed within the plasmachamber, and must function consistently and properly. To be costeffective, such components must often withstand hundreds or thousands ofwafer cycles while retaining their functionality and cleanliness. Onesuch component, the electrostatic chuck, is used to retain asemiconductor wafer or other workpiece in a stationary position duringprocessing. The electrostatic chuck provides more uniform clamping thanchucks employing mechanical clamping, and can operate in vacuum chamberswhere a vacuum chuck cannot be used. However, variations in aspects ofthe clamping can cause undesirable process variations within a wafer.

SUMMARY

A method of modifying the heat transfer coefficient profile of anelectrostatic chuck by configuring the areal density of a mesaconfiguration of an insulating layer of the chuck is provided. The heatconduction at a given site can be measured by use of a heat flux probe.The probe is placed on the insulating surface of the chuck and overliesa plurality of mesas in a single measurement. A plurality ofmeasurements across the chuck surface provide a heat transfercoefficient profile from which a target mesa areal density isdetermined. Using the target areal density, a mechanical correction canbe made to one or more locations of the mesa configuration on the chuck.The contact area of the mesas within the local measurement area isreduced by an amount sufficient to change the local mesa areal densityto the desired mesa areal density. This can be accomplished using any ofknown techniques for controlled material removal such as laser machiningor grit blast machining on an X-Y table.

A method of modifying the capacitance profile of an electrostatic chuckby adjustment or initial fabrication of the height of a mesaconfiguration of an insulating layer of the chuck is also provided. Atarget mesa height can be determined by use of a capacitance probe. Theprobe is placed on the insulating surface of the chuck and overlies aplurality of mesas in a single measurement site. A plurality ofmeasurements across the chuck surface can be made to provide acapacitance profile from which a target mesa height is determined. Usingthe target height, a mechanical fabrication or correction can beeffected at each of the measurement sites. This can be accomplishedusing any of known techniques for controlled material removal.Furthermore, transitions between regions of different heights can besmoothed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a schematic of a cross section of an exemplaryelectrostatic chuck with mesas, showing a conductive base and aninsulating layer.

FIG. 2 depicts a plan view of the chuck of FIG. 1, showing a mesaconfiguration and a continuous edge region.

FIG. 3 shows an exemplary heat flux probe including a heater block, amechanism to apply force, an HFT and silicon piece.

FIG. 4 shows the heat flux probe of FIG. 3 placed on the electrostaticchuck of FIG. 1 and heat flow.

DETAILED DESCRIPTION

Plasma processing apparatuses for semiconductor substrates, such assilicon wafers, include plasma etch chambers which are used insemiconductor device manufacturing processes to etch such materials assemiconductors, metals and dielectrics. Components of plasma processingapparatuses include electrostatic chucks, which are used to retainsemiconductor wafers or other workpieces in a stationary position duringprocessing. Electrostatic chucks (ESC) provide more uniform clamping andbetter utilization of the surface of a wafer than mechanical chucks andcan operate in vacuum chambers where vacuum chucks cannot be used. Ingeneral, electrostatic chucks comprise an electrically insulating layerover a conductive body, the conductive body in electrical contact to oneor more electrodes, to which a chucking voltage is applied. The wafer ismaintained in position against the insulating layer by an attractivecoulombic force. The shape of the chuck may include a conventional diskcommonly used in plasma etching systems and the chuck may be supportedin the chamber by various arrangements, such as by using a cantilever.The insulating layer may have grooves, mesas, openings, recessedregions, and like features.

As demands on process outputs such as wafer uniformity increase, thewafer chuck is required to deliver higher performance. For example,process control problems in critical etch applications call for improvedcontrol of temperature and capacitance across the wafer. Error in theaccuracy of lateral dimensions in some etch processes can be sensitiveto temperature and be up to +/−1 nm/° C. A desirable control of lateralfeatures of 1-2 nm therefore requires temperature uniformity andrepeatability of less than 1° C. Some types of electrostatic chuckscomprise multiple component parts, each introducing some error. Forexample, a tunable electrostatic chuck is a complex structure whichinvolves the ESC ceramic, a bond to an aluminum plate, a thin filmheater, a bond to a baseplate, and the baseplate itself. Deviations fromuniformity for each component of the structure may contribute to agreater overall deviation. A compensation for natural variation in themanufacturing process applied to electrostatic chucks which may comprisemultiple components would be advantageous.

In manufacturing a chuck with a mesa configuration, 21, the fabricationprocess generally comprises the removal of material at the surface ofthe insulating layer to a depth of about 5 μm to about 40 μm, such thatsmall area features (“mesas”) are left to support the wafer 11. Mesascan be of virtually any size, shape and arrangement. For example, mesascan be elliptical, polygonal or torroidal, have vertical or slopedwalls, the top surfaces can be concave, flat or convex, and the cornerscan be sharp or rounded. The mesas can take on a “bump” shape wherein apartial spherical shape is emerging from a flat surface. A preferredmesa shape, size and arrangement, is circular with vertical walls, adiameter of about 1 mm, a spacing of about 5 mm, substantially coveringthe ESC surface, respectively 21. A continuous sealing high area 12, 22is often retained at or near the wafer edge so as to maintain thepressure of a heat transfer gas such as helium used to enhance thermalconductivity. In such a configuration, typically about 3% to about 10%of the chuck surface is mesas and the sealing area at the edge.Advantageously, mesa designs facilitate backside particle reduction andimprove dechucking.

The mesas and sealing area are generally formed from one or more layersof an electrically insulating material. Examples of such insulatingmaterials include, but are not limited to, silicon nitride, silicondioxide, alumina, tantalum pentoxide, and the like.

FIGS. 1 and 2 show a version of an electrostatic chuck assembly whichuses mesas. The electrostatic chuck assembly 10 comprises a conductivesupport 18, an electrically insulating layer 19, high areas of theelectrically insulating layer 13, 23, and low areas of the electricallyinsulating layer 14, 24. The conductive support 18, formed of aconductive metal such as aluminum, is electrically connected to an RFcircuit of a plasma processing apparatus (not shown) for plasmaprocessing a workpiece, such as a 200 mm or 300 mm wafer. In theelectrostatic chuck assembly 10 in FIG. 1, the lower surface 15 of theinsulating layer 19 is in contact with the conductive support 18. Thehigh areas 13 of the insulating layer 19 support a semiconductorsubstrate (not shown). A thermocouple 105 is incorporated into theconductive support 18 for temperature measurements. Cooling channels 17are provided in the conductive support 18 for supply of temperaturecontrol fluids or gasses. In particular, conductive support 18 ispreferably adapted to accept a temperature control unit, or TCU (notshown) which is capable of maintaining the temperature of the conductivesupport to a desired temperature by use of fluid flowing through arecirculation loop.

Preferably, the aluminum support 18 is about 1.5 inches thick. Thesupport has boss 16 designed to underlie a wafer and has a height ofabout 0.5 inches. For example, to support a 200 mm or smaller diameterwafer, the boss is preferably circular with a 200 mm diameter. Theinsulating layer 19 is preferably ceramic such as alumina or AlN, with athickness of preferably less than about 5 mm thick, more preferablyabout 1 mm thick. The dielectric layer could be a plasma spray material,for example, alumina over an aluminum substrate. The thickness of thealumina is preferably about 25 mils (635 μm), and, in any event, must bethick enough to allow for the creation of mesas as high as 200 μmwithout losing physical or electrical integrity either during themanufacturing process or during use.

A preferred embodiment involves a modification of a mesa configurationof an ESC to achieve a target etch profile across the wafer surface. Amesa configuration can be described using two primary dimensions: mesaheight and mesa area. In embodiments, control of mesa area is used as amechanism to control temperature, and control of mesa height is used asa mechanism to control capacitance. An assessment of each mechanism ismade separately. A preferred embodiment of a method to controltemperature through the adjustment of mesa area is given in Example 1,and preferred embodiments of methods to control capacitance throughadjustment or initial fabrication of mesa height are given in Examples 2and 3. The examples are intended to be illustrative rather thanexclusionary:

Example 1

During normal plasma processing, such as plasma etching, the plasma actsto heat the wafer. The temperature fluctuation of the wafer is thereforea function of heat flow out of the wafer. According to the theory ofheat flow, heat transfer can occur in three ways: conduction, convectionand emission of radiation. For the following assessment, emission ofradiation is neglected. A heat transfer coefficient K is defined as aheat flow per unit of temperature difference between two bodies. K of awafer on a chuck with mesas can be determined by considering the highand low areas as two cases: 1) the heat transfer that occurs over a lowarea, and 2) the heat transfer that occurs over a high area (mesa). Inthe case of the low area, the heat transfer occurs through a mechanismof energy transfer from the wafer at the higher temperature to the gas,and from the gas to the ceramic layer. Even though the gas may be in thefree molecular flow regime (mean free path much greater than the size ofthe container), for this assessment, this mechanism of heat transfer isclassified as convection. In the case of the mesa, due to surfaceroughness of the ceramic, direct contact between the ceramic and thewafer occurs over an area which is less than the nominal contact area(the high area). Gas is present interstitial to the contact points andcontributes to the heat transfer through convection. Thus the heattransfer occurring over a mesa is due to both contact (conduction) andthrough the gas (convection). Conduction due to contact is presentwhether or not gas is present, but convection does not occur in the lowareas when gas is not present. When gas is present, both mechanismsexist in the high areas, suggesting that heat transfer increases withincreasing high area. Thus the local heat transfer rate is adjustable bymodifying the mesa area locally, that is, increasing the proportion ofmesa area increases the heat transfer rate whereas reducing theproportion of the mesa area reduces the heat transfer rate.

A heat flux probe can be used to measure both heat flux and local wafertemperature. For the present assessment, operation of a heat flux probecan be carried out in one of two ways: 1) by measuring the wafertemperature at a given heat flux; or 2) by adjusting the heat flux tothat which is required to achieve a desired wafer temperature, forexample a uniform temperature. In both cases the measurements take placeat a plurality of sites, typically such that the sites are arranged inan ordered grid pattern which generally covers the chuck. Preferably, atleast 10 mesas are included in each single measurement, more preferably,at least 30 mesas are included. In the first case a temperature profileresults, and in the second case a heat flux profile results.

In a preferred embodiment, a temperature profile is generated and theinformation is used to generate a heat transfer coefficient (HTC)profile. The HTC profile is then used to alter the insulating layer toeffect alteration in the heat flux across the wafer. For example, theinsulating layer can be altered to compensate for observed variation inthe temperature profile. In alternative embodiments, the insulatinglayer can be altered to compensate for observed variation in an etchprofile of a semiconductor wafer.

An exemplary embodiment of a preferred probe 31 for heat fluxmeasurement is shown in FIG. 3. The probe consists of a verticalcylindrical stack of about 1″ diameter, although the cross-sectionalshape of the probe is not restricted to circular. The probe could have asquare, rectangular, triangular or any polygonal shape in cross-section.At the top of the stack, a heater block 32 is situated, the heater blockcomprising an embedded small adjustable heater and thermocouple 33, theheater having a maximum power output of about 50 watts. Exemplaryheaters such as the ¼″ diameter, 0.25 mm thick, 279232 CIR-1016 120V 50W cartridge heater are available from Chromalox, Inc., Pittsburgh, Pa.Attached proximate and below the heater block is a Heat Flux Transducer(HFT) 34, comprising a thin sheet of controlled thermal resistancematerial. Temperature sensors 35 form a thermopile, and are attached tothe top and bottom surfaces of the HFT. Heat flux transducers like theone shown in FIG. 3 are commercially available, for example, the modelBF-04 HFT from Vatell Corp, Christiansburg, Va. Heat Flux Transducersare available in different sizes, and provide a reading of the flux, forexample, in mV/(W/cm²), as well as the lower sensor temperature. Anamplifier, such as the AMP-12 from Vatell (not shown) is usedcooperatively with the HFT.

In order to simulate the measurement of a silicon wafer, attachedproximate and below the HFT is a piece of silicon wafer 36, ofapproximately the same area as the HFT. A temperature measurement fromthe lower sensor is therefore a measurement of wafer temperature. Bothattachments to the HFT are made with high thermal conductivity bondingmaterials. A downward force can be applied to the probe to facilitatecontact. For example, an amount of force may be used to approximate thatof the ESC clamping force, e.g. 40 Torr. In the probe 31, the downwardforce is represented by deadweights 37 and a mechanism to evenlydistribute the downward force 38, but other mechanisms to apply anddistribute force could be used as well. Additionally, the chucktemperature is preferably held constant during the measurement.

A depiction of an exemplary probe disposed on an exemplary chuck isshown in FIG. 4. Heat flux Q 41 flows from the heater block through thewafer piece and into the chuck over a probe area A_(p). Both Q and A_(p)are treated as constants for the purpose of this assessment. Thetemperature difference 42 between the conductive support and the waferis denoted by ΔT, and an effective heat transfer coefficient within theprobe area is denoted by K_(eff). K_(eff) can be determined by treatingconduction through contact and convection through the gas separately.Using subscripts “c” and “g” to refer to contact and gas, respectively,K_(c) is then the heat transfer coefficient due to contact and K_(g) isthe heat transfer coefficient due to the gas. The initial Mesa ArealDensity α_(i)=A_(i)/A_(p) is the initial fraction of the insulatinglayer of the chuck within the probe area which has a raised surface innominal contact with the wafer piece, and α_(f) is the final Mesa ArealDensity having a raised surface in nominal contact with the wafer pieceafter the preferred adjustments have been made. Nominal is used to meanthe planar-equivalent surface of the mesa at the top, where the mesasupports the wafer. In other words, ignoring roughness andnon-parallelism, α is the total cross-sectional area of the mesas withinthe probe area A_(p) at the supporting surface of the wafer. Thus mesaconfigurations of differing detailed geometry, e.g. square vs. circularcross section or vertical vs. sloped walls, need not have differing α.For a given probe measurement, α_(f) is sought to determine the targethigh area, and thus the amount by which the high area under the probemust be reduced in order to achieve the desired temperaturedistribution. An equation providing α_(f) for a given probe measurementarea is determined as follows:

In a preferred embodiment, a target HTC in a localized area of the mesaconfiguration is achieved by removal of material. In accordance with theabove discussion, a removal of material will result in a reduction ofheat flux from the wafer and thus an increase in wafer temperature.Therefore using material removal alone, a desired wafer temperature canbe achieved by selecting a target ΔT that is at least as high as thehighest of the measured ΔT's. A target ΔT for all sites across the chuckis thus chosen and denoted ΔT_(o), and will, in general differ from themeasured ΔT's, individually denoted by ΔT_(m), by an amount denoted by∈, wherein:

∈=ΔT _(m) −ΔT _(o).  (1)

The objective of the adjustment is then to bring ∈ to zero. Defining qas the heat flux per unit area, the general heat transfer equation isgiven as

q=Q/A _(p) =ΔT×K _(eff).  (2)

As mentioned above, the effective heat transfer coefficient K_(eff) iscomposed of two components: the convection-only heat transfer in the lowregions, and the conduction plus convection heat transfer in the highregions. For the case where the contact area is much smaller than thenon-contact area (comprising both the low area and the high area not incontact), K_(eff) for the target configuration can be expressed asK_(g)+α_(f)K_(c). A desired heat flux Q is selected by varying the probeheater power and choosing a value which results in a clear readingeverywhere on the chuck, and one which shows a clear difference betweenregions with different mesa areal densities. An exemplary heat flux isfrom about 0.2 to about 2.0 W/cm², and the temperature of the heater isdetermined by the heat flux.

Denoting the initial effective heat transfer coefficient byK_(i)=q/ΔT_(m), and using the target value of K_(eff) of q/ΔT_(o), Eqn.1 can be rewritten using Eqn. 2 as:

∈=q/K _(i) −q/( K _(g)+α_(f) K _(c)).  (3)

Defining γ to be K_(g)/K_(c) and rearranging Eqn. 3,

α_(f)=(∈/q)γK _(i)+α_(i)/[1−(∈/q)K _(i)].  (4)

The set of K_(i) determined for the plurality of measurement sites,along with the x-y coordinates of each K_(i) can be used to determine anHTC profile. Additionally, using Eqn. 3, the set of K_(i) taken togetherwith the set of ∈ can be used to determine K_(eff) for the targetconfiguration, and thus a target HTC profile. Similarly, the set ofα_(f) determined for the plurality of measurement sites along with thex-y coordinates of each α_(f) determine the areal component of thetarget mesa configuration.

For a given chuck, γ is assumed to be constant. This is because primaryfactors inherent in K_(c) are evidently the material itself and thesurface finish of the material, both of which are preferably constantfor a measurement made from anywhere on the chuck. K_(g) is a functionof the material and the gas pressure used, which are also assumed to beconstant. Furthermore, γ is determinable by measuring K at differentlocations with different and known mesa areal densities, and solvingindependently for K_(g) and K_(c). For this assessment, therefore, γ isassumed to be known and constant.

The testing can be carried out in an apparatus that would allow forsupport of the chuck as well as enablement of the desired testconditions. An appropriate apparatus comprises a vacuum test chamberconfigured to maintain the chuck at a set temperature and capable ofbackfill of a heat conducting gas. The apparatus is preferably capableof supporting and numerically controlling x-y positioning of a heat fluxprobe as well as capable of applying a contact force of the probe ontothe chuck. The apparatus is also preferably capable of registering andrecording measurement data signals from the probe, as well aselectronically determining the target mesa configuration from the data.

The measurement areas can overlap or can be separated by a distance. Theregions between measurement areas can be adjusted to interpolated arealdensities or to gradual transitional densities such that no abruptchanges in density and thus in HTC occur. Interpolation can be effected,for example, by changing areal density linearly between two differentdensities. In general, if the density transitions from site to site aretoo abrupt, a finer measurement grid and/or a small probe diameter maybe required. Adequate readings may be obtained by allowing somemeasurement sites to be omitted, or by making measurements in anirregular pattern.

All of the factors required to determine α_(f) have thus beendetermined. Based on all prior discussion, a preferred embodiment of aprocess involving reducing the localized mesa area of an ESC to achievea target HTC profile across a wafer placed on a chuck comprises thefollowing experimental procedure:

-   -   1. Size a heat flux probe so that its mass results in a force on        an ESC approximating that of the ESC clamping force, e.g. 40        Torr.    -   2. Place the ESC to be tested in a vacuum chamber, keeping the        temperature of the conductive support constant by employing a        TCU.    -   3. Position the probe at the measurement site on the chuck        surface.    -   4. Evacuate the chamber and backfill to the desired helium        pressure, e.g. 20 Torr.    -   5. Select the desired heat flux Q.    -   6. Calculate q from Q using the known A_(p).    -   7. Measure and record the resultant wafer piece temperature and        conductive support temperature, thus determining K_(i)=q/ΔT_(m)        for all sites on the grid.    -   8. Select a target ΔT=ΔT_(o) and determine ∈ for each site.    -   9. Use Equation 4 to determine α_(f) for all sites on the grid.        Check that α_(f) is always less than α_(i)

A mechanical correction can now be made to the chuck to achieve a moreuniform thermal conductivity across the chuck. The mesa areal densitywithin the measurement area is adjusted to reduce the contact area by anamount sufficient to change the local α_(i) to α_(f). This canconveniently be accomplished using any of known techniques forcoordinate controlled material removal, where removal is effected, forexample, by routing, laser machining or grit blast machining, andcoordinate control is effected by the use of an X-Y table. Areareduction can be carried out by reducing the area of any number of mesaswithin the measurement area, or removing some mesas completely, or anycombination thereof. The area reduction process is repeated for eachprobe measurement site.

After completion of mechanical correction and achieving α_(f) at allmeasured sites, the overall process could be repeated to achievecompliance to a predetermined tolerance band around ΔT_(o). It isappreciated that robotics and machine control computers can be used toautomate this procedure.

In plasma etch chambers, bias RF power can be adjusted based on avoltage probe measurement attached to an electrostatic chuck electrode.An error in the voltage measurement may affect the etch process.Furthermore, variation in topography of the electrode relative to thewafer may lead to a variation in the local sheath potential, andconsequently in the etch process performance as well. In a plasmareactor, an ESC may be considered to comprise part of a capacitativecircuit, wherein the plasma is the first conductor, the insulating layerof the ESC is the dielectric, and the conductive body of the ESC is thesecond conductor. A preferred embodiment involves the local modificationof a mesa configuration of an ESC to achieve more uniform etchconditions across the wafer surface. The local modification is theadjustment of mesa height to control capacitance. Another preferredembodiment involves the initial fabrication of a mesa configuration ofan ESC to achieve uniform etch conditions across the wafer surface.

A capacitance probe is preferably used on an ESC to measure thecapacitance between the probe head and the conductive body. Capacitancemeters of sufficient accuracy of +/−1 pF or better can be used, such asthe Protek CM110 available from Testextra LLC, Freehold, N.J. The meteris used in conjunction with a probe, which is preferably about 1″ indiameter, and comprises a metal cylinder which has a plastic handleextending out of the top. Using the capacitance probe, a measurement ismade at preselected points on the ESC. Preferably, the preselectedpoints form a regular grid pattern, allowing for the determination of acapacitance profile, i.e. a profile of capacitance across the chuck.Assuming a plurality of mesas is included in the measurement, the highand the low areas of the mesa array will contribute differently to themeasured capacitance reading.

Example 2

This example is for the initial fabrication of mesas, where initialcapacitance measurements are made before mesas have been fabricated,i.e. when the surface of the insulating layer is planar. Mesas arefabricated by removing material from the area where there are no mesas.Areas which become mesa areas remain untouched, and provide the higharea upon which the wafer is supported. A determination of depth isdeveloped in accordance with a procedure in which the Mesa Areal Densityis known (provided by the above discussion), and mesas are going to be,but have not yet been, fabricated at a certain height. Assuming that themesa area is small compared to A_(p), we write a capacitance equationwhich relates only to the low areas. Using notation C_(g) for thecapacitance due to the gap (the area that will be between the mesas whenthey are formed), and C_(i) for the capacitance of the insulating layerbelow the gap, then the target capacitance C_(T) (i.e. the capacitanceof the area between mesas achieved at the desired mesa height) can beexpressed as

1/C _(T)=1/C _(g)+1/C _(i).  (5)

From C=∈A/d:

∈_(o) A _(p) /C _(T) =d _(g) +d _(i)/∈_(i),  (6)

where ∈_(i) is the dielectric constant of the insulating layer, d_(i) isthe thickness of the insulator below the gap, and d_(g) is the height ofthe gap. At the onset of the procedure, the capacitance is measuredwhile the surface is flat, so C_(m), the measured capacitance is givenby:

C _(m)=∈_(o) A _(p)∈_(i)/(d _(g) +d _(i)).  (7)

Solving Eqns. 6 and 7 for d_(g) gives:

d _(g)=∈_(o) A _(p)[(1/C _(T)−1/C _(m))/(1−1/∈_(i))].  (8)

Eqn. 8 thus provides a desired mesa height within each measurement arearesulting in the determination of a C_(m), for the case where the mesasare not present prior to the fabrication. The set of C_(T) determinedfor the plurality of measurement sites, along with the x-y coordinatesof each C_(T) can be used to determine a target capacitance profile.Additionally, the set of d_(g) determined for the plurality ofmeasurement sites along with the x-y coordinates of each d_(g) determinethe height component of the target mesa configuration.

A mechanical fabrication can now be carried out on the chuck to achievethe desired capacitance profile across the chuck. Preferably, mesas arethen created within the measurement site by removing material in thearea that will become the low area around the mesas to a depthsufficient to change the local C_(m) to C_(T). The depth of the materialremoval is preferably from 5 μm to 40 μm, and more preferably from 5 μmto 20 μm. This can conveniently be accomplished using any of knowntechniques for coordinate controlled material removal, where removal iseffected, for example, by routing, laser machining or grit blastmachining, and coordinate control is effected by the use of an X-Ytable. The machining process is repeated for each probe measurementsite.

The measurement areas can overlap or can be separated by a distance. Theregions between measurement areas can be fabricated to interpolateddepths or to gradual transitional depths such that no abrupt changes indepth and thus in capacitance occur. Interpolation can be effected, forexample, by changing depth linearly between two different depths. Ingeneral, if the depth transitions from site to site are too abrupt, afiner measurement grid and/or a small probe diameter may be required.Adequate readings may be obtained by allowing some measurement sites tobe omitted, or by making measurements in an irregular pattern.

All of the factors required to determine d_(g) have thus beendetermined. Based on the above discussion, a preferred embodiment of aprocess involving initially fabricating the mesa height of an ESC toreduce a capacitance variation across a wafer placed on a chuckcomprises the following procedure:

-   -   1. Fabricate the ESC up to just prior to mesa fabrication.    -   2. Measure the capacitance from the surface to the conductive        body using a suitable probe over a pre-defined measurement grid        to determine the set of C_(m).    -   3. Determine a pre-defined target capacitance C_(T).    -   4. Use Eqn. 8 to determine the set of d_(g), the target depth at        each measurement site.    -   5. Create the mesas at each site by machining.    -   6. Adjust the machining processing in a continuous fashion to        gradually transition from site to site to achieve the desired        local mesa height.

Example 3

In the case where the mesas already exist on the chuck, an adjustment ofmesa height to achieve a desired capacitance profile may be needed. Inone embodiment, C_(T) is chosen so that the target capacitance profileis uniform across the chuck. In order to achieve a final uniformcapacitance most efficiently it is useful to determine the relationshipbetween material removal and capacitance. From Eqn. 6, above, thecapacitance due to the low area is given by∈_(o)A_(p)/(d_(g)+d_(i)/∈_(i)). Since the sum of d_(i) and d_(g) is aconstant, the capacitance can be rewritten as∈_(i)∈_(o)A_(p)/[d_(g)(∈_(i)−1)+h], where h=d_(i)+d_(g). For dielectricmaterials, ∈_(i) is greater than 1, so ∈_(i)−1 is positive. Thus it canbe seen that an increase in the gap depth will result in a decrease inthe capacitance. Thus in the preferred embodiment, where material isonly removed, capacitance can only be reduced. The selection of C_(T) inthis case, therefore, is preferably equal to or less than the lowestmeasured capacitance from all selected sites.

A mechanical correction can now be made to the chuck to achieve thedesired capacitance profile across the chuck. Preferably, mesas are thenadjusted within the measurement site by deepening material around themesas to a depth sufficient to change the local C_(m) to C_(T). This canconveniently be accomplished using any of known techniques forcoordinate controlled material removal, where removal is effected, forexample, by routing, laser machining or grit blast machining, andcoordinate control is effected by the use of an X-Y table. The machiningprocess is repeated for each probe measurement site.

The measurement areas can overlap or can be separated by a distance. Theregions between measurement areas can be adjusted to interpolated depthsor to gradual transitional depths such that no abrupt changes in depthand thus in capacitance occur. Interpolation can be effected, forexample, by changing depth linearly between two different depths. Ingeneral, if the depth transitions from site to site are too abrupt, afiner measurement grid and/or a small probe diameter may be required.Adequate readings may be obtained by allowing some measurement sites tobe omitted, or by making measurements in an irregular pattern.

Based on the above discussion, a preferred embodiment of a processinvolving adjusting the mesa height of an ESC to reduce a capacitancevariation across a wafer placed on a chuck comprises the followingprocedure:

-   -   1. Measure the capacitance from the surface to the conductive        body using a suitable probe over a pre-defined measurement grid.    -   2. Determine a pre-defined target capacitance C_(T).    -   3. Determine whether the depth needs to be increased or        decreased for each grid site.    -   4. Adjust the mesa height at each site by machining such that        C_(m) approaches C_(T).    -   5. Repeat the process as needed until all sites are within a        desired tolerance of C_(T).    -   6. Adjust the machining processing in a continuous fashion to        smoothly transition from site to site to achieve the desired        local mesa height.

With the methods described above, it is possible to providecustomization of electrical and thermal properties of an electrostaticchuck for the purpose of achieving a target heat transfer coefficient orcapacitance profile.

The present embodiments have been described with reference to preferredembodiments. However, it will be readily apparent to those skilled inthe art that it is possible to embody the invention in specific formsother than as described above without departing from the spirit of theembodiment. The preferred embodiment is illustrative and should not beconsidered restrictive in any way. The scope of the embodiment is givenby the appended claims, rather than the preceding description, and allvariations and equivalents which fall within the range of the claims areintended to be embraced therein.

1. An electrostatic chuck made by: making a plurality of localizedmeasurements at a plurality of locations on an exposed surface of aninsulating layer of the electrostatic chuck; determining the target mesaconfiguration using the measurements; and fabricating a mesa pattern inthe exposed surface of the insulating layer such that the mesa heightcorresponds to the target mesa configuration.
 2. The electrostatic chuckof claim 1 wherein the target mesa configuration is determined from atarget heat transfer coefficient profile.
 3. The electrostatic chuck ofclaim 1, wherein the target mesa configuration is achieved by reducing amesa contact area at one or more of the locations.
 4. The electrostaticchuck of claim 1 wherein the measurements are made using a heat fluxprobe.
 5. The electrostatic chuck of claim 1 wherein the target mesaconfiguration is determined from a target capacitance profile. 6.(canceled)
 7. The electrostatic chuck of claim 5 wherein the targetcapacitance profile is achieved by increasing the height of a mesaconfiguration.
 8. The electrostatic chuck of claim 1 wherein themeasurements are made using a capacitance probe.
 9. The electrostaticchuck of claim 1 wherein the surface of the insulating layer includes amesa pattern, the method further comprising removing insulating materialto achieve a mesa contact area corresponding to the target mesaconfiguration.
 10. The electrostatic chuck of claim 4 wherein thesurface of the insulating layer includes a mesa pattern and at least 1,at least 3, at least 5, or at least 10 mesas are included in the heatflux probe measurement.
 11. The electrostatic chuck of claim 1 whereinthe target mesa configuration comprises mesas are eliptical, torroidaland polygonal cross-sectional shapes.
 12. The electrostatic chuck ofclaim 1 wherein the target mesa configuration comprises mesas having amaximum dimension in cross-section of about 0.1 mm to about 10 mm. 13.The electrostatic chuck of claim 1 wherein the target mesa configurationcomprises a spacing between mesas of from about 0.5 mm to about 5 mm.14. The electrostatic chuck of claim 1 wherein the measurements aretaken at a plurality of locations arranged in a grid pattern.
 15. Theelectrostatic chuck of claim 1 wherein the electrostatic chuck includesfluid channels adapted to cooperate with a temperature control unit tocontrol the temperature of the chuck.
 16. The electrostatic chuck ofclaim 9 wherein the insulating layer of the chuck is less than 5 mmthick.
 17. The electrostatic chuck of claim 4 wherein the heat fluxprobe applies a force of 10 Torr to 100 Torr to the insulator surface.18. The electrostatic chuck of claim 4 wherein the plurality ofmeasurements are carried out in a vacuum chamber backfilled with heliumat a pressure of 2 Torr to 200 Torr.
 19. The electrostatic chuck ofclaim 18 wherein the probe is moved by a numerically controlledpositioning apparatus so as to obtain a heat transfer coefficientprofile of the surface of the chuck.
 20. The electrostatic chuck ofclaim 3 wherein the target mesa configuration is fabricated routing,laser machining and/or grit blasting.
 21. The electrostatic chuck ofclaim 1 further comprising customizing a preexisting mesa pattern tocorrespond to the target mesa configuration by routing, laser machiningand/or grit blasting.
 22. (canceled)
 23. The electrostatic chuck ofclaim 1 wherein the transition of depth of regions between measurementareas in the exposed surface of the insulating layer is gradual.
 24. Theelectrostatic chuck of claim 8 wherein the surface of the insulatinglayer includes a mesa pattern and at least 1, at least 3, at least 5, orat least 10 mesas are included in the capacitance probe measurement. 25.The electrostatic chuck of claim 3 wherein the electrostatic chuck islocated in the interior of a plasma processing chamber.
 26. A method ofprocessing a semiconductor wafer using the electrostatic chuck of claim1, comprising clamping a semiconductor wafer on the chuck and plasmaprocessing the semiconductor wafer.
 27. (canceled)
 28. (canceled)
 29. Aprobe comprising a heater, a heat flux transducer and a silicon piece,wherein the approximate maximum dimension of the cross-sectional area ofthe probe is 0.5″, 1.0″, 1.5″, or 2.0″.